The present invention relates to an automatic sampler for providing samples to an analyzer, such as a gas chromatograph and a liquid chromatograph.
An example of an automatic sampler which performs triaxial operations or movements in a cylindrical coordinate system is shown in FIG. 4. In the automatic sampler, around a cylindrical arm stand 3 for mounting an arm 2 at an upper end thereof, there is disposed a rack 4 in a disc shape, which is lower than the arm stand 3. The rack 4 is provided with a plurality of vial holes 4a on a ring-shaped upper surface thereof, and vials 5 can be inserted into the respective vial holes 4a. The vial 5 is a glass bottle containing a liquid sample, and on an upper end thereof, a cylindrical resin cap 5a is fitted. Incidentally, the cap 5a is provided to attach a rubber disc for closing an upper end opening of the vial 5, and in order to stick a needle to the rubber disc for sucking the liquid sample, a hole is formed in a center part of the cap. In the example of FIG. 4, in each of the rows arranged in the radial directions with an adequate angle on the upper surface of the rack 4, five vial holes 4a are formed at equal intervals. Also, an upper portion of the vial hole 4a is enlarged to have a tapered shape so that the vial 5 can be easily inserted therein.
The arm stand 3 rotates in a .theta. axis direction with respect to a lower stand, not shown, and at the same time, the arm stand 3 can move vertically or up and down in a Z axis direction. The arm 2 is provided with a gripper 1 (sample holding section) for holding the vial 5 at a longitudinal rod-shaped distal end. And, the arm 2 slides in the radial direction of the arm stand 3, i.e. it is movable in an R axis direction. Thus, by the arm 2 and the arm stand 3 (mechanism for moving the holding section), the gripper 1 can freely move (including rotational movement) above and around the rack 4 in the triaxial directions of the cylindrical coordinate system formed of the .theta. axis direction, the Z axis direction, and the R axis direction.
The gripper 1 at the distal end of the arm 2 has four fingers 11 projecting downwardly, and by changing the width of a space or distance between these fingers 11 to be narrower or wider by a holding mechanism, the cap 5a of the vial 5 can be held or released. In the holding mechanism of the gripper 1, as shown in FIG. 5, two frames 12, each having two fingers 11 projecting downwardly, are fitted with two rods 13 so as to be slidable in the right and left directions. Also, in these two frames 12, racks 12a are disposed at upper and lower sides to project toward each other, and engage a pinion 14 disposed therebetween. The pinion 14 is a gear attached to a distal end of a square bar 15 which is freely rotatable and disposed in the longitudinal direction in the arm 2 shown in FIG. 4, and is driven from a side of the arm stand 3 through a bevel gear, not shown, fitted with the square bar 15. Thus, in the holding mechanism of the gripper 1, when the pinion 14 is rotated through the square bar 15 by driving force from the side of the arm stand 3, the space between the two frames 12 is expanded or reduced, so that the space between the two pairs of the fingers 11 extending from the two frames 12 can be expanded or narrowed.
In the automatic sampler as described above, the arm stand 3 is firstly elevated in the Z axis direction and then rotated in the .theta. axis direction, and at the same time, the arm 2 is moved in the R axis direction, so that the gripper 1 is located above the aimed or target vial 5. Then, after the space between the two pairs of the fingers 11 in the gripper 1 is expanded, the arm stand 3 is lowered in the Z axis direction to the holding position. Accordingly, as shown in FIG. 6, four fingers 11 with the expanded space therebetween are arranged so as to surround the cap 5a of the vial 5. Then, when the square bar 15 is rotated to close the space between the two frames 12 so that the space between the two pairs of fingers 11 is narrowed, as shown in FIG. 7, the cap 5a of the vial 5 is clamped and held among these four fingers 11. And, when the arm stand 3 is again elevated in the Z axis direction, the vial 5 in which the cap 5a is held by the fingers 11 of the gripper 1 is lifted up from the vial hole 4a in the rack 4. Further, by rotating the arm stand 3 in the .theta. axis direction and simultaneously moving the arm 2 in the R axis direction, the held vial 5 can be transferred to an analyzer or the like. Also, the vial 5, with which the process at the analyzer is finished, can be returned to the original vial hole 4a by reverse operations as described above.
As an alternate structure of the gripper 1 of the automatic sampler, there is a structure wherein a fork-shaped pawl is inserted from a side under the edge of the cap 5a to lift the cap 5a. If the above described gripper 1 is used, however, since it is required to have a wide space for sliding the pawl on the side of each vial 5, the vials 5 can not be closely disposed on the rack 4, so that a number of the vials 5 to be set would become extremely small. Also, instead of the gripper 1 using the aforementioned four fingers 11, there is a gripper using three fingers 11. In order to hold the periphery of the vial 5 from the three directions by using the gripper with three fingers 11, however, it is required to provide spaces for inserting the respective fingers 11 between the vials 5 in the three directions on the rack 4. On the other hand, if the vials 5 are arranged in a row normally, there are spaces for inserting the fingers 11 at four corners, so that in order to increase the number of the vials 5 which can be set on the rack 4 with the same area, using the four fingers as described above is advantageous.
In the aforementioned automatic sampler, the arm stand 3 is rotated in the .theta. axis direction and the arm 2 is moved in the R axis direction, so that the cap 5a of the aimed vial 5 is disposed in the center of the four fingers 11 of the gripper 1. However, since there is a mechanical error between the position of the gripper 1, which is located by moving the arm stand 3 in the .theta. axis direction and by moving the arm 2 in the R axis direction, and the actual position of the vial hole 4a on the rack 4, the cap 5a of the vial 5 is not always disposed at the center of the four fingers 11 of the gripper 1. Normally, however, as shown in FIG. 8, even if the cap 5a of the vial 5 is deviated from the center of the four fingers 11, as a distance between the two pairs of the fingers 11 decreases, the vial 5 is pushed by the finger 11 abutting or contacting the cap 5a at first (finger 11 located at upper right portion in FIG. 8) to move toward the central side of the four fingers 11, so that the accurate holding is possible.
As shown in FIG. 9, however, in case the position of the cap 5a of the vial 5 is deviated from the center of the four fingers 11, for example, toward the upper portion in the figure, the two fingers 11 in the upper side in the figure abut against the side surface of the cap 5a substantially at the same time from the right and left directions, so that there is a possibility that the cap 5a is clamped and held between these two fingers 11 without moving. Especially, in case silicone rubber or the like covers around the fingers 11 to increase frictional resistance for preventing the vial 5 from slipping off from the space between the fingers 11, even if the vial 5 is clamped between the two fingers 11, the vial 5 is not moved toward the central side smoothly. Thus, there is a high possibility that the vial 5 is caught between the fingers 11 and held therebetween incompletely. Namely, the reason why the vial 5 moves toward the central side is that when the fingers 11 push the cap 5a, sliding occurs between the fingers 11 and the cap 5a. Therefore, when silicone rubber or the like covers the periphery of the fingers 11, sliding of the cap 5a is deteriorated, and the cap 5a is held incompletely.
Also, in the case shown in FIG. 8, when the vial 5 pushed by one finger 11 is not fully moved to the central side, as in the case of FIG. 9, the vial 5 is held by the two fingers 11. And, if the cap 5a of the vial 5 is held only by the two fingers 11 as described above, there is a possibility that when the vial is ascending in the Z axis direction, holding of the vial 5 is failed and the vial 5 can not be lifted up, or even if the vial 5 is held, when the vial is transferred or moved thereafter, holding of the vial 5 becomes unstable, so that the vial 5 is inclined or slipped on the halfway.
Therefore, in the conventional automatic sampler, when the gripper 1 holds the vial 5, if the vial 5 is not smoothly moved to the central side as a result of being pushed by the fingers 11, the vial 5 can not be securely held.
Incidentally, the aforementioned problem is not limited to the case of holding the vial 5 on the rack 4, but may occur similarly in the case of holding the vial 5 to return the vial 5 with which the steps or processes at the analyzer or the like are finished. Also, the gripper 1 is not limited to the case of using the four fingers 11, but also the same problem occurs as in the case of using three fingers 11 or five or more fingers 11.
Accordingly, the present invention has been made in view of the aforementioned problems, and an object of the invention is to provide an automatic sampler, which can always securely hold the sample.
Another object of the invention is to provide an automatic sampler as stated above, in which an elastic member is freely rotatably fitted onto the periphery of each finger of a sample holding section.
Further objects and advantages of the invention will be apparent from the following description of the invention.